Numerical Simulation Of Ductile Fracture Research Articles

Numerical simulation of ductile fracture in polyethylene pipe with continuum damage mechanics and Gurson-Tvergaard-Needleman damage models

A phenomenon-based hybrid approach of experimental testing and finite element simulations is used to describe the fracture behavior of pipe-grade polyethylene. The experimental testing adopts a modified D-split test method to stretch the pipe ring (notched pipe ring) specimens that have symmetric, double-edged flat notches along the pipe direction. Two series of experimental testing were conducted: (1) monotonic loading till fracture and (2) monotonic loading to a predefined strain level, keeping constant displacement for a period of time, and then unloaded. Crosshead speeds of 0.01, 1, and 100 mm/min were used in both series of tests. Likewise, two series of finite element simulation were conducted to establish the constitutive equations, either with or without considering damage evolution during the deformation process. The constitutive equation without the consideration of damage was established using results from the first series of experimental testing, and that with damage was inspired from the second series which showed the decrease in unloading modulus with the increase of crosshead speed or the predefined strain level. The results show that with the consideration of damage evolution, the constitutive equations enable the finite element simulation to determine the whole stress–strain relationship during both necking and fracture processes.

A non-linear ductile damage growth law at elevated temperature

Continuum damage mechanics (CDM) model is commonly used for the prediction of ductile fracture. For numerical simulation of ductile fracture in impact or high-temperature problems, the damage growth law that incorporates the effect of high temperature is needed. Experimentally, it has been observed that damage growth decreases with temperature. However, the damage growth law at high temperature is not easily available in the literature. In the present work, a damage growth law at high temperature is proposed for steel, based on the experimental measurement of damage carried out at IIT Kanpur.

Numerical simulation of ductile fracture based on mean field homogenization method: Modeling and implementation

A mean filed homogenization method at large deformation is presented to describe the damage softening effects due to nucleation and growth of voids during ductile fracture. The developed homogenization frame is combined with the Nucleation-And-Growth model and the percolation theory based coalescence model for describing ductile damage evolution. A semi-implicit numerical algorithm is developed to solve the ductile damage model. Based on the model, we have carried out numerical simulations of the spall fracture of a Al 2024-T4 plate and a Ti–6Al alloy plate under impact loads. The simulated free surface velocity profiles show good agreement with experimental measures.

Numerical Simulation of Ductile Fracture in Modified Arcan Test

In this study, the experimental results from a modified Arcan test on dual-phase steel are revisited in order to assess a numerical modelling approach for ductile fracture. This experiment is chosen since it displays a complex crack-path that undergoes three phases: fracture initiation and crack propagation with transition from Mode I to Mode II. A significantly larger amount of plastic dissipation is observed in the material at the point of fracture initiation compared to the material points along the crack-path. A numerical approach that is capable of capturing this complex crack-path is believed also to give good predictions in other complex fracture problems. The numerical simulations of the modified Arcan test are run with the nonlinear Finite Element (FE) code IMPETUS Afea Solver. Elements with tri-linear shape functions are utilized in combination with explicit time integration. The plastic behaviour of the material is modelled by the elastic-viscoplastic J2 flow theory using the Voce work-hardening rule. Both element erosion and node-splitting techniques are tested in order to simulate the crack propagation. It is shown that the node-splitting technique with a crack-tip enhancement gave the best prediction of the three different phases of the crack propagation.

Numerical Simulation of Ductile Fracture in Cylindrical Tube Impacted Against a Rigid Surface

Impact of tubes has an extensive application in crashworthiness. Analytical and numerical studies on axial impact of tubes have been carried out mostly at low-to-moderate impact velocities at which only the buckling of tubes is observed. However, experimental observations show that tubes fracture when the impact velocity is high. The objective of this article is to study the fracture of cylindrical tubes impacted against a rigid surface by numerical simulation. First, through-the-thickness fracture at the impacted end is simulated at the impact velocity of 350 m/s. Then, a detailed parametric study is carried out with respect to various parameters like the friction coefficient, tube thickness, tube length, and impact velocity. With an increase in the friction coefficient, the spread of fracture is more toward the outer edge. Further, the spread of fracture toward the inner edge takes place in an inclined manner. At higher tube thickness, the spread of fracture ceases after some time without reaching the inner edge. The tube length is found to have no effect on the fracture. It is observed that the fracture spreads faster with the impact velocity.

Numerical simulation of ductile fracture with the Rousselier constitutive law

This contribution aims at developing robust and reliable tools dedicated to predictive numerical simulation of ductile fracture. Description of damage mechanisms relies here on the Rousselier constitutive law. To achieve robustness and objectivity, several points need then to be addressed: reduction of the set of internal variables so as to recast the model into the framework of generalised standard materials; proper expression of the normal plastic flow rule at the vertex of the yield surface; finite strain formulation based on a multiplicative split of the deformation gradient; fully implicit integration of the constitutive equations leading to a single scalar equation that admits a unique root; use of mixed finite elements to avoid volumetric locking; strain gradient-based nonlocal model to control strain localisation and remedy spurious mesh dependency. The capabilities of the resulting numerical formulation are demonstrated through simulating the cup–cone fracture of a notched tensile specimen.

On some topics for the numerical simulation of ductile fracture

In this work, we analyze some aspects of the macroscopic Gurson–Tvergaard–Needleman (GTN) constitutive model when it is addressed to solve ductile fracture problems by means of numerical simulations: (i) The analytical solutions of the material discontinuous bifurcation problem is performed. Closed and exact formulas are obtained. The so determined critical conditions and the developed strain localization mode are afterward studied and compared in crack growth problems. Even when this methodology of analysis is rather standard at the present, the conclusions drawn from this study differ significantly from that obtained with a similar analysis in quasi-brittle fracture problems. (ii) A new very robust numerical integration method for the GTN model, namely the Impl–Ex Method, is proposed. It is a low computational cost algorithm, equivalent to a linear problem per each integration step, with a reasonable precision for engineering purposes. Its accuracy and convergence rate is assessed by means of an error study applied to a ductile fracture test simulation. (iii) A detailed analysis of a plane strain ductile crack growth problem is performed in a material containing two size-scale of voids. In the analysis, particular attention is given to the mesh size dependence and to the coalescence of the larger void.

A numerical approach for the simulation of ductile fracture with embedded discontinuities

AbstractIn the present study, a computational approach for the numerical simulation of ductile fracture within the framework of the finite element method is proposed. In the developed macroscopic formulation, the inelastic behavior in the bulk of the material is described by the finite elasto‐plastic material model proposed in [4]. The failure process is modeled by introducing discontinuities when a special local fracture criterion is satisfied. The discontinuities are incorporated via special triangular finite elements with embedded interfaces following the line of [2]. Finally, the numerical procedure is evaluated for a twodimensional representative test problem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical Simulation of Ductile Fracture Based on Local Approach Concept

In this paper a finite-element analysis on ductile fracture in two-dimensional quasi-static state is performed by using the local approach concept in continuum damage mechanics. An isotropic damage model based on the generalized concept of effective stress is proposed. Crack propagation is achieved by removing critically damaged elements. The finite-element approximation of a largely deforming body based on the incremental total Lagrangian concept is carried out. As numerical examples, the mesh size sensitivity analysis and the simulation of the shearing mode failure in plane strain state are carried out to verify the present formulation qualitatively. For an edge cracked plate under plane stress state, load-displacement curves and successively fractured shapes are shown. It can be concluded that the proposed model may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

Numerical simulation of ductile fracture during high strain rate deformation

A numerical integration scheme is presented for integration of the pressure-sensitive yield criterion due to Gurson, suitable for explicit dynamic finite element calculations. This scheme utilizes a sub-increment approach to Mayntain stability for the large strain increments and intense triaxiality that can occur under high strain rate loading. A number of validation problems are presented after which two laboratory-scale high strain experiments are simulated. The integration scheme is shown to be stable and to capture the onset of tensile fracture under high strain rate loading conditions.